Technical White Paper: Lowering Springs and Bump Stops, Take Three
After playing with various suspension set ups over the past two years (H&R, Dinan, Moton Street Sport, and soon Moton CS), I've learned quite a bit about this M3's suspension, and I thought it's time to write another article regarding the highly contentious topic of lowering springs and bump stops.

I will attempt to do this with no equations and pure common sense.

Bump Stops

Bump stops, as most of you know, are engineered elastomers. The main advantage of bump stops vs. a traditional spring is that the former can be engineered to provide variable stiffness at a very light weight.

In the old days bump stops are simply installed to prevent the suspension from topping or bottoming out; they do not affect the suspension except at the limits of travel. However, modern day bump stops have started to play an increasingly more important role on street cars, especially on a every day sports car like the M3.

Comfortable on the Street and Handles Well on the Track

The E9x M3 has been praised by almost all car magazines in the world as the best all-around sports car on the market today... because you can comfortably take your kids to school and then pass everyone on the race track.

The M3 is comfortable on the street because its springs are relatively soft, both the front and rear have wheel rates (lb/in) in the mid-hundreds. Having soft springs means that the wheels have greater travel with less abrupt transitions over bumps, which eliminates the rough ride experienced dedicated track cars.

But softer springs are not usually well suited for the race track, because they allow too much suspension travel when the car is under high G forces, i.e. in a corner, or under braking, and this prolongs transitions and unsettle the platform.

M3's Bump Stops

The extensive use of bump stops is one reason why the M3, even with a very comfortable ride, can handle the race track so well.

As Steve Dinan has pointed out, there is only about 0.5" of suspension travel before the front bump stops come into play; a similar situation applies for the rear.

This is exactly the intention of the BMW engineers.

These bump stops are engineered so that they are initially very soft (compressible by hands), but as compression increases, they get progressively harder. The bump stops gradually increase the effective wheel rate to control suspension travel and maintain the platform of the car.

This is how the M3 gets away with soft springs.

The "Cardinal Sin" of Riding on Bump Stops

Bump stops have become a catch phrase for those who are considering lowering springs. Dinan has of course extensively used "modified bump stops" as the chief marketing slogan for why their kit is superior.

But as I have explained above, even in stock form, the M3 is designed to ride on its bump stops more often than you think.

Consider this, when there are four people in a car, your M3 will be already on its bump stops... and that is perfectly OK, as the bump stop is initially very soft.

What is NOT OK
Excessive lowering: M3's bump stops are initially very soft, but when compressed to a certain length, they will become very stiff.

This is why it is not a good idea to excessively lower your M3 with spring kits. The M3 has roughly 2.25 inches of compression travel. If you lower too much you would be constantly bottoming out on the bump stop.

Uneven front/back lowering: the M3 is designed to be pretty neutral (with slight understeer) at the limit. The point here is that the front and rear suspension are balanced to produce this effect. If one end of the car is lowered significantly more than the other, that axle will likely bottom out, loose grip sooner, and change the balance of the car.
My Recommendations
Do your research!
Be moderate when lowering!
Have a qualified mechanic install your kit.

Remember, it is OK to ride on bump stops, but ride with good judgement.
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If you have a competition package, stay away from the Eibach springs, it will actually raise the rear of your car slightly and is replacing the springs with a softer springs too.

The best and better matched springs for ZCP cars are the H&R springs. Stay away from RD Sport.

Hey there guys, quick question, I have a 2011 E92 M3 with Comp pkg. Which springs would best fit my car so I get a nice hight (a little lower than what I have now)? I heard if you have comp pkg, putting springs on will actually raise the car? Also, putting springs on the car, is it true it messes up the dampeners/struts?

Hey there guys, quick question, I have a 2011 E92 M3 with Comp pkg. Which springs would best fit my car so I get a nice hight (a little lower than what I have now)? I heard if you have comp pkg, putting springs on will actually raise the car? Also, putting springs on the car, is it true it messes up the dampeners/struts?

I don't have any engineering knowledge, but the H&R plus springs on the E92 M3 I drove at VIR a couple of years ago did great with stock EDC suspension. I'm torn between those and the Eibachs now because I don't know if I can go 1.2" lower (H&R) with the roads here.

Can anyone comment on a few owners assertation of the eibach springs feeling "bouncy"?

I have EDC and it's not bouncy at all , I love the ride , I could have went with a more aggresive looking drop but it would've probably compromise the ride and to me it was not worthy ! A quick shot of my car with newly installed cf splitters and spoiler !

^^Correct. Slightly lower with Eibachs over ZCP. I am currently running HnR's with e36 bumpstops and its a decent drop and very easy to DD.

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BEFORE YOU BUY YOUR NEXT BMW, PM ME FIRST WE CAN HOOK YOU UP!Jimmy Bach: jbach@stevethomasbmw.com - Cell:805-807-1989
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